To study the effect of immunization with pneumococcal polysaccharide (PS) before pregnancy on the subsequent antibody response of neonates to PS antigens, female mice were given various doses ranging from 0.5 to 50 %g or more of pneumococcal polysaccharides, e.g. type 19A, 19F or 3 PS, before mating. After birth the young mice were divided into two groups. One group was given an additional dose of PS (0.1 %g) at two wks of age. The young mice that were born to PS-treated female mice and that received an additional dose of PS had stronger antibody response than those that did not receive an additional dose of PS. Treatment of female mice with 500 %g induced a suppression of the antibody response in maternal and young mice. Young mice from mothers that received hormone treatment, such as growth hormone, or estrogen followed by pneumococcal vaccine during pregnancy, produced higher IgM antibody responses to 19A PS. GRANTZ01BA02020 Immunization of mice with inactivated pneumolysin (ply) has been shown to increase the survival time after challenge with virulent pneumococci. Thus, inactivated ply can serve as an effective protein carrier for pneumococcal polysaccharide (PS)-protein conjugate immunogens. Inactivated type 1 pneumolysin, prepared from E. coli clone pJCP20 was conjugated to pneumococcal type 19F PS by the cyanogen bromide activation of PS and carbodiimide coupling method for conjugation. 30- 50% protein was contained in the 19F PS-protein conjugate. The antibody response of 19F PS-ply conjugate was measured by radioimmuno-assay. Various doses of conjugate from 0.5 to 50 mg were injected into mice at 8 wks of age. A booster injection of 5 mg was given either once at 7 days, or twice at 7 and 14 days after primary injection. Seven days after last injection the antibody response was measured. The results showed that the conjugate immunogen induced significantly higher 19F Ab levels in the mice than were obtained with 19F PS. The 19F Ab levels in mice that received two booster injections were incresed more than 20 fold over the control group that received 19F PS alone. The antibody response to pneumolysin and protection against challenge of virulent pneumococci will be determined in mice receiving 19F PS-ply conjugate.